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  1. #1
    Join Date
    1st January 2003
    Posts
    17

    Multi Purpose or Multi Motor rockets

    An observation after several years of going to local launches I see that most Rocketeers tend to build their rockets with very
    limited capabities. As an example take a 2.1" airframe how many
    builders out there design and build it so it can fly on a 29,38,54 mm motor? Or how about Night flights and mounting a strobe light
    nose cone or have a removable ballast tube that can adjust the CG if necessary.

    I would like to hear your thoughts as to why or why not to design
    this way?

    Cheers David
    ARSA member # 366
    TRA # 10710 L1
    NAR #78678-SR L1

  2. #2
    Join Date
    13th December 2009
    Location
    Union, OH
    Posts
    4,568
    I think alot of people are still learning and are building kits to gain experience before they start modifying kits/designing scratch built rockets for more than one flight configuration. Also, I think alot of people build bigger rockets for specific reasons - i.e. "this is my level 2 rocket", "this is for my first 54mm motor", things like that.


  3. #3
    Join Date
    18th January 2009
    Location
    Boulder
    Posts
    12,502
    I don't see any need to build every 2.1 inch rocket for a 54mm (minimum diameter). Some rockets are not built for altitude, and it takes a lot more money, skill, and time to properly do a minimum diameter than it does to do a simple sport rocket of the same diameter.
    NAR #84281 L3
    TRA #11233 L3

  4. #4
    Join Date
    19th January 2009
    Posts
    606
    Why would 2.1" diameter rocket have to handle 29, 38, and 54mm motors? That's a tough build there. Anything light enough to fly on 29mm is just going to scream on any 54mm. Then you'd also have to have a place to fly it. If you don't have a big waiver on your usual field why build rockets designed to bust it? Then you just have to screw around with adapters and such for most of your flights.

    Night flights are relatively rare. No way I'm going to spend the extra time and effort building night capability into every rocket when I'll make maybe one night flight a year.

    Many people do have adjustable ballast in the nose but, unless you are absolutely tweaking your airframe for a specific goal, it isn't necessary. Well it probably would be if you designed every rocket to handle 29-54mm motors because the motor mass and lifting capability will change a lot along that spectrum. Otherwise, ss long as the rocket is stable it's good.

    I guess for me it comes down to an old anecdote, " Things designed to do everything rarely do anything well."

  5. #5
    Join Date
    3rd February 2002
    Posts
    653

    Re: Multi Purpose or Multi Motor rockets

    Originally posted by Airdale
    An observation after several years of going to local launches I see that most Rocketeers tend to build their rockets with very
    limited capabities. As an example take a 2.1" airframe how many
    builders out there design and build it so it can fly on a 29,38,54 mm motor?
    Most everything I build includes more motor tube than I plan to use, although I don't typically use the entire airframe diameter. But, for example, if I'm planning to use 38's, I'll try to put in a 54mm MMT, in case I get the urge down the road. I think you'll find that pretty common with veteran rocketeers who all know the old saying, "You can always adapt down, but going the other way is pretty tough."

    Completely max'ing it out is something different. A 54mm minimum diameter bird will surely be out of sight at apogee, so the likelihood of losing it is high. That's not appealing to most, although I do know a couple of rocketeers who have flown such beasts including 4" birds with 98mm motors and 6" birds with 150mm motors.

    At the MR level, there are lots of underpowered kits. Big Daddies, Big Berthas and Fay Boys are easily up-motored without risking loss. Lots of folks will go up at least one motor diameter step over stock.

    Inexperience builders tend to follow the instructions closely, but as they gain more experience, they look for new challenges. I think you'll find that folks who've built more than a few rockets do indeed upgrade kits for bigger motors along with recovery system improvements, electronics bay additions, etc.

    Doug

  6. #6
    Join Date
    18th January 2009
    Location
    Boulder
    Posts
    12,502
    Big bertha's DEFINITELY need a 24. E6's are beautiful in them, and F39's kick them nice and hard
    NAR #84281 L3
    TRA #11233 L3

  7. #7
    Join Date
    21st January 2009
    Location
    San Diego, CA
    Posts
    2,859
    When I built my L1/L2 cert rocket, I specifically modified it to include the adaptability you are talking about. It has a 54mm mount, but flew L1 on a 29mm, L2 on a 38mm, and can handle a baby 54mm. It's not glassed, so I'm not eager to go and see just how much power it can take, but I'm pretty confident that it can handle a K.

    To accommodate the added weight of the motor, I installed a removable and adjustable noseweight system using a piece of all-thread epoxied into the nosecone. Weighted "donuts" can be added to the all-thread and held in place with a washer and a wingnut. The recovery device attaches to a removable eye-bolt that threads onto the end of the all-thread.

    I think that one of the main reasons more people don't take this approach is that it does require some extra work, and that to make a rocket light enough to fly on small motors but strong enough to fly on big ones can be a very narrow field.

    WW
    NAR L2/#84763 - DART #317

  8. #8
    Join Date
    22nd July 2005
    Posts
    10

    Multi-purpose rockets

    Until I actually stepped on the fin can the other day, I was almost done with a "modular" rocket for my L1 cert.

    I have little opportunity to fly at waivered sites, so my "big" rockets are all LMR's.

    I use the rear separation idea from Stu Barrett over at Info-central. You can build a generic booster section and have different forward airframes. Or, a few nuts around the inside of the coupler and you can "bolt" a standard or piston recovery airframe to the booster. It seems to be a versatile modular design idea, as well as being "anti-zipper".

    I've built a 4XBP cluster booster section and now I need another 29mm booster. I just may make the new booster 38/29mm, as you suggest.
    MisterB

    Entropy just isn't what it used to be.

  9. #9
    Join Date
    24th September 2010
    Location
    Victoria's Secret
    Posts
    4,243
    I'd rather have a versitile fleet than a versitile rocket.

    Personal preference, I suppose.

    So I want to fly 2000' + on an F? Got a rocket for that.

    So I want to fly 900' on an H? Got a rocket for that.


    So I want apogee deploy on an I436T and get it back on the field we'er flying from today? got it covered.

    How about a cloud buster on an H112J? Got it covered.


    We could go on and on.


    I'd rather have a versitile fleet than just one rocket. Personal preference.

  10. #10
    Join Date
    7th July 2006
    Location
    SW Ohio
    Posts
    1,075

    Re: Multi Purpose or Multi Motor rockets

    Originally posted by Airdale
    An observation after several years of going to local launches I see that most Rocketeers tend to build their rockets with very
    limited capabities. As an example take a 2.1" airframe how many
    builders out there design and build it so it can fly on a 29,38,54 mm motor? Or how about Night flights and mounting a strobe light
    nose cone or have a removable ballast tube that can adjust the CG if necessary.

    I would like to hear your thoughts as to why or why not to design
    this way?
    '

    Actually there is a thread similar to this in the Techniques section where I talk about adjustable nose ballast. As I read your post I have become inspired to build a fully lit bird for a night flight so perhaps that is what the hobby needs; a little inspiration.
    Mike
    NAR #86177
    TRA #16435
    L1 with Loc Precision H76 Vulcanite on H73J (2,109') 7/23/06
    L2 with Binder Design Velociraptor on K695R (6,171' @ 716mph) 9/20/15
    L3 with Polecat Aerospace 10" Nike Smoke on M2500T (6,468' @ 556mph) 11/26/16 (RIP 5/26/17 :cry:)

    Current Projects:
    Waive Goodbye (design around 18k waiver)

  11. #11
    Join Date
    1st January 2003
    Posts
    17

    Multi Purpose or Multi Motor rockets

    I would like to say thanks to all that have responded.

    I can now see that as you might say, I look at the world a little
    differently than most. And yes it is fun to build a std. Big Daddy and launch it with your kids or just for the shear pleasure of doing so by your self or with adult friends.

    Again thanks for your thoughts

    Cheers David
    ARSA member # 366
    TRA # 10710 L1
    NAR #78678-SR L1

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